1. Field of the Invention
The present invention relates to a system and method of controlling a permanent magnet synchronous motor, and more particularly to a system and method of controlling a permanent magnet synchronous motor to maximize use of voltage created by a battery via voltage phase control within a weak magnetic flux area and to achieve compensation for a torque error through a torque compensator when driving the permanent magnet synchronous motor for a hybrid vehicle.
2. Description of the Related Art
In general, an interior permanent magnet synchronous motor (IPMSM) is a type of synchronous motor in which a permanent magnet inside the rotor core. IPMSMs are often used for industrial purposes or in hybrid electric vehicles due to their excellent high speed durability and high speed drivability.
FIG. 6 for example shows a block diagram illustrating an existing control method for an IPMSM. A control device for a PMSM 10 provides a final magnetic flux-axis (D-axis) command voltage Vdsr* and a final rotational force-axis (Q-axis) command voltage Vqsr* to a PWM inverter and includes a current command generator 12, a current controller 14 for controlling current, a light modulator (not shown), and a feedback controller 16.
The current command generator 12 generates a magnetic flux-axis (D-axis) command current idsr* and a rotational force-axis (Q-axis) command current iqsr* based on the maximum magnetic flux |λ|max of the results of controlling the command rotational force Te* and the weak magnetic flux.
The current controller 14 generates a primary magnetic flux-axis (D-axis) command voltage (Vdsr*) and a primary rotational force-axis (Q-axis) command voltage (Vqsr*) based on the magnetic flux-axis (D-axis) command current (idsr*) and a rotational force-axis (Q-axis) command current (iqsr*) from the current command generator 12.
Moreover, the feedback controller 16 performs a PI current control-based weak magnetic flux control in order to control the magnetic flux in the permanent magnet synchronous motor 10 and generates a maximum magnetic flux deduction proportional to the D-axis command voltage Vdsr* and the Q-axis command voltage Vqsr*. In this case, when the D-axis command voltage Vdsr* and the Q-axis command voltage Vqsr* are fed back from the current controller 14, a square average generator 16a of the feedback controller 16 outputs an output value as expressed by equation 1.√{square root over (vdsr*2+vqsr*2)}  [Equation 1]
The output value as expressed by equation 1 is subtracted from the maximum combined voltage
      v          s      ,      max        =            v      dc              3      by a subtractor 16b of the feedback controller 16 wherein Vdc is a direct current link voltage applied to the PWM inverter 18, and the feedback controller 16 outputs the subtracted output voltage as a rotor angular velocity Δidsr* of the permanent magnet synchronous motor.
FIG. 7 shows maximum use of voltage during the PI current control-based weak magnetic flux control of the permanent magnet synchronous motor. More specifically, reference numerals V1 to V6 indicate voltages represented by a vector sum of the D-axis applied voltage Vdsr* and the Q-axis applied voltage Vqsr*, the area of a circle inscribed in a hexagonal area indicates an area in which linear voltage synthesis is enabled, and
      v          s      ,      max        =            v      dc              3      indicates a maximum linearly synthesized voltage available within the circular area. Moreover, the hexagonal area indicates an area in which voltage synthesis is available by a spatial vector pulse width modulation (PWM) and a hatched area excluding a circular area inside the hexagonal area indicates a non-linear voltage modulation area.
In an existing permanent magnet synchronous motor, when a voltage is generated and a torque control is performed within the voltage limiting circle (the circular area) as the linear voltage area, that is, the maximum synthesized voltage
      v          s      ,      max        =            v      dc              3      where the linear voltage synthesis is enabled for the purpose of stable current control, there are several problems when as follows.
First, since voltages in the area inside the circle inscribed in the hexagon, as illustrated in FIG. 2, are used as a weak magnetic flux reference voltage, the voltage use decreases by about 10% than when voltages in the hexagonal area are used. Second, since the inverter cannot generate a precise voltage when the maximum synthesized voltage is greater than the maximum voltage
      v          s      ,      max        =            v      dc              3      in the voltage limiting circle (the area inside the circle) and deviates from the inscribed circle of the hexagon (the circular area) during the voltage modulation, the linearity of the output voltage (the maximum synthesized voltage) is broken and unstable torque control arises. Thus, it is difficult to control a synchronous motor stably while operating the motor at high speeds.